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(A) Trajectory of Hayabusa spacecraft to Itokawa. The view is looking down on the ecliptic plane from the north. The Sun is at (0,0). Reddotted part along the spacecraft trajectory denotes the thrust direction of ion engines is northward, while other southward. (B) The spacecraft undertook a tour near the asteroid after achieving the home position observation. The view is from the Sun. The asteroid and the home position are overlapped at the origin. Arrows indicate the sequential path of the spacecraft. Dots show the hovering sites. Each spacecraft position indicated by the number in the figure corresponds to the dates that follow: position (1), 8 to 10 October, westward, high phase angle; (2), 12 and 13 October, zero solar phase angle; (3), 15 October, east side high, phase-angle; (4), 17 and 18 October, south pole; (5), 20 October, south pole, low altitude (È4 km); (6), 22 October, north pole, low altitude (È4 km); (7), 23 and 24 October, north pole; (8), 27 and 28 October, low altitude observation (È3 km). Dashed lines include low-altitude observation.
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During the interval from September through early December 2005, the Hayabusa spacecraft was in close proximity to near-Earth
asteroid 25143 Itokawa, and a variety of data were taken on its shape, mass, and surface topography as well as its mineralogic
and elemental abundances. The asteroid's orthogonal axes are 535, 294, and 209 meters, the mass is...
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1] Newly obtained gravity and topography data of the Moon, combined with a lithospheric flexure model that considers both surface and subsurface loading, are used to place constraints on the density of the upper crust from a localized spectral admittance analysis. Subsurface loads are found to be relatively unimportant in the highlands, and when su...
Citations
... This paper is motivated by the formation circumstances of small, rubble pile asteroids. In Fujiwara et al. [4] the current state of the asteroid Itokawa is hypothesized to have arisen from the aftermath of a cataclysmic collision between two larger asteroids, as depicted in Fig. 1. While the formation of rubble pile bodies from such collisions has long been suspected [22,21], the Hayabusa mission to Itokawa provided the first tangible example of what such a system would look like, with the body clearly being a contact binary of two bodies, apparently formed separately before coming into contact. ...
... In the decades since these results, observations of other asteroid systems have only reconfirmed the basic morphology types shown in these rubble pile asteroids. Figure 1: Presumed formation mechanism for the small rubble pile asteroid Itokawa [4]. ...
This work analyzes the energetics of asteroid rubble piles in order to understand what asteroid morphologies should naturally arise from their formation and evolution process. In doing this, a phase diagram is developed that maps out the range of final minimum energy states that a collapsing gravitational aggregate can achieve as a function of total angular momentum and mass distribution. This is developed assuming properties associated with rubble pile asteroids, and can provide insight into the formation and subsequent evolution of contact binaries and orbital binaries in the solar system as an outcome of catastrophic disruptions. The system angular momentum is used as an independent parameter, combined with resulting minimum energy configurations as a simple function of mass morphology of the final system. The configuration of systems with an energy boosted above the minimum energy state are also considered. This paper considers an ideal case, but outlines general results that can be continued for more precise models of distributed granular media modeled using continuum models or using discrete element models.
... Spacecraft missions have encountered several bilobed small bodies, which include comets [1], asteroids [2,3], a trans-neptunian object 486958 Arrokoth [4], and most recently, the moonlet of a binary asteroid Dinkinesch | Selam [5], alluding to a substantial population at large [6]. The shape may indicate separate origins of individual objects before their merger in the aftermath of a nondestructive collision or accretion [7,8,9]. ...
... Even with an erroneous density of 530 kg m 3 (and the assumption of homogeneous distributions), the errors were mitigated by accounting for the higher-degree EH coefficients as opposed to omitting them entirely. With the exception of 163 % and 20 % at (1,2) and (2,5), respectively, for lobe 1, 1 the errors were reduced to the order of 1 %. The lobes' mass were in particular well resolved within an accuracy of 1 %. ...
... Even with an erroneous density of 530 kg m 3 (and the assumption of homogeneous distributions), the errors were mitigated by accounting for the higher-degree EH coefficients as opposed to omitting them entirely. With the exception of 163 % and 20 % at (1,2) and (2,5), respectively, for lobe 1, 1 the errors were reduced to the order of 1 %. The lobes' mass were in particular well resolved within an accuracy of 1 %. ...
Bilobed bodies represent a significant class of small extraterrestrial objects in the Solar System. We present a double harmonic-series approach to model the gravity of the lobes separately, thereby allowing their mass distributions to be constrained independently. We study an exemplary candidate contact binary, comet 67P/Churyumov-Gerasimenko, and establish two ellipsoidal harmonic series referred to the closest-bounding, non-overlapping ellipsoids of the respective lobes. We show that the model is more robust near the irregular body shape than a global spherical harmonic series, which is a customary product determined from spacecraft tracking. While they can be estimated directly from measurements, we demonstrate here that the double series can also be transformed from an existing spherical harmonic model by means of decomposition. We use simulations to analyze model solutions for a few heterogeneous mass distributions.
... For example, asteroid 2016HO3, which the China National Space Administration plans to explore, has a gravity of approximately 1.1 × 10 − 5 m/s 2 (micro-gravity) [6], and just a little information about the surface environment of 2016HO3 can be obtained. To date, only a few missions have focused on small-body sampling, including the Hayabusa series of the Japan Aerospace Exploration Agency (JAXA) [7][8][9][10][11] (Fig. 1A), the Philae mission of the European Aviation Agency [12,13] (Fig. 1B), and the OSIRIS-REx mission of the National Aeronautics and Space Administration [14] (Fig. 1C). ...
... Interestingly, Torifune has several common points, such as albedo, reflectance spectrum (Fig. 13), size, and shape, with (25143) Itokawa, visited by the Hayabusa spacecraft in 2006 (Fujiwara et al. 2006). Itokawa is a rubble-pile elongated asteroid, which is classified as an Sq-type asteroid, with the most likely composition similar with LL chondrites (Binzel et al. 2001b). ...
The near-Earth asteroid (98943) Torifune, previously designated 2001 CC, is the flyby target of the Hayabusa2 extended mission, nicknamed Hayabusa2 (SHARP: Small Hazardous Asteroid Reconnaissance Probe). The ground-based telescope observations offer a key science input for the mission's scientific investigation. During 2022 - 2024 this asteroid was at visible apparent magnitudes brighter than 18.5, allowing for a detailed characterization using ground-based telescope observations. We determined its rotation period h and its absolute magnitude H = 18.78 0.14 and. The large number of lightcurves allows to estimate its axes ratio, its convex shape and its pole orientation , and which indicate a prograde rotation. We report the semi-axis of the equivalent ellipsoid, a = 0.42 km, b = 0.16 km, and c = km. Consequently, the volume equivalent diameter is = km . Using observations conducted simultaneously with four broadband filters, we determined mag, mag, and mag. Additionally, we found that Torifune exhibits no detectable large-scale heterogeneity. We classified the object using a high signal-to-noise ratio spectrum (over the visible and near-infrared region) as Sq-type in the Bus-DeMeo taxonomy. We estimate a mineralogy similar to LL/L ordinary chondrites, with an ol/(ol+px) = 0.60, a Fa content of 28.5 mol, and a Fs content of 23.4 mol. The spectral data indicate a surface affected by moderate space weathering effects.
... While these spectra are relevant for interpreting surfaces of larger, regolith-rich planetary bodies, such as the Moon, recent missions have shown that smaller (<1 km) near-Earth asteroids (NEAs) such as Itokawa, Bennu, Ryugu, Didymos, and Dimorphos show a greater diversity of grain sizes (A. Fujiwara et al. 2006;D. S. Lauretta et al. 2019;S. ...
Linking near-Earth asteroids to associated meteorites can be a challenging process for many reasons, one being grain size differences. To address this issue for rarer meteorites, we studied visible and near-infrared (0.35-2.5 μm) reflectance spectra of 11 rare meteorite classes over five different grain size bins (45-90 μm, 90-150 μm, 150-300 μm, 300-500 μm, and 500-1000 μm). We analyzed the reflectance properties, diagnostic spectral band parameters (band centers and band area ratios), spectral slope, and taxonomic classification. The spectra were analyzed using principal component analysis to detect trends in principal component (PC) space and the impact on asteroid taxonomic classification in the Bus-DeMeo system. We found that the absolute reflectance (visual albedo) at 0.55 μm (photometric V band) typically decreases with increasing grain size, although there are some variations such as sharp increases for the slabs. Our EH4 and aubrite show a trend of increasing spectral slope with decreasing grain size. Our ureilite, angrite, winonaite, acapculoite, and mesosiderite show a general trend of a decrease in Band I (∼0.9 μm) depth with increasing grain size up to 500-1000 μm. Taxonomic classification of spectra of all grain sizes shows that classification tools generally struggle to differentiate grain size effects from mineralogical variations. This research demonstrates the need for a more robust taxonomic classification system that accounts for grain size and one that accurately classifies small near-Earth asteroids with regolith-free surfaces.
... Given that the effective quality factor of Eros' interior is most similar to the scattering quality factor of planetary regolith 37 , our analysis suggests that Eros is a rubble pile or, at the very least, the Eros interior responds to exterior stresses similar to a rubble pile. However, we caution that a rubble-pile interior model for Eros would be fundamentally different than what is commonly envisioned for smaller kilometre-scale rubble piles visited by spacecraft [16][17][18] . For Eros, the scattering length solution, L s = 0.5 ± 0.1 km, suggests that the Eros interior contains large blocks that may span the entirety of the smaller kilometre-scale asteroids. ...
An asteroid’s interior dictates how its space environment changes its shape and surface, which provides a record of the collisional and dynamical evolution of the Solar System. Knowledge of asteroid interiors also enables the formulation of mitigation strategies against hazardous asteroids. Despite this importance, asteroid interiors remain poorly understood. Asteroids between 0.2 km and 10 km in diameter are thought to have rubble-pile interiors, transitioning to fractured interiors at 10 km scales, then to coherent and differentiated interiors at ≳100 km scales. The asteroid 433 Eros, the only 10-km-scale asteroid explored by a rendezvous mission, is an exemplar of asteroids at intermediate scales. Recent exploration of smaller rubble piles has provided insight into physical properties that are shared with Eros-sized objects. Here we quantify the seismic and physical properties of Eros’ interior through measurements and modelling of crater degradation and erasure from the impact that formed the 7.5-km-diameter Shoemaker crater on Eros. Our results indicate that Eros’ deep interior has a seismic wave scattering length of 0.5 ± 0.1 km and effective quality factor EQ < at frequencies >0.06 Hz. Contrary to the established view of Eros as a fractured shard, our findings suggest that Eros’ interior properties are consistent with those of a rubble-pile asteroid.
... This study is focused on investigating kinetic impact effects on a Dimorphos-like (∼160 m diameter) target, which is relevant for planetary defense applications. Four of the five asteroids that have had spacecraft rendezvous are rubble piles: Itokawa (A. Fujiwara et al. 2006;J. Saito et al. 2006), Bennu (D. S. Lauretta et al. 2019), and Ryugu (S. ...
... Watanabe et al. 2019), with bulk porosity estimations of ∼41% (A. Fujiwara et al. 2006), 25%-50% (O. S. Barnouin et al. 2019a), and >50% (S. Watanabe et al. 2019), respectively. ...
... The specific setup and structure of a given rubble pile will also affect how a crater forms following a hypervelocity impact. Some asteroids are seen to have smoother regions ("ponds") surrounded by rockier (and rougher) areas (e.g., Itokawa (A. Fujiwara et al. 2006;J. Saito et al. 2006) and Eros (A. ...
Rubble pile asteroids consist of reassembled fragments of once larger monolithic asteroid parent bodies. Recent spacecraft missions to asteroids like Itokawa, Ryugu, Bennu, and Dimorphos suggest that rubble pile asteroids are common in the asteroid population, and rubble piles could be a likely structure among potentially hazardous objects. Therefore, it is important to understand the response of rubble pile targets to kinetic impacts for potential future deflection needs. The recent Double Asteroid Redirection Test (DART) mission motivates an investigation of kinetic impacts into rubble pile targets to understand their effects on deflection. Here, we simulate kinetic impacts into Dimorphos-sized asteroid targets to understand the effect of the impact site structure on the deflection efficiency of relevant sizes for planetary defense. We perform 52 two-dimensional simulations where we vary the impact site structure of the impact site, the target porosity, and the material behavior/strength model to understand their relative effects on crater size and the momentum enhancement factor ( β ). We find that the effects of the impact site on both crater size and β are greatest for impacts into weaker targets, where impact sites rich in matrix material result in statistically larger craters and higher β s compared to impact sites rich in boulder material. Further, impact site structures that promote increased boulder ejection result in larger β values. These results provide important intuition to understand the DART impact and to extrapolate results to future potential missions.
... A simple estimate of the approximate bounds on the range of Roche Limits for breakup of an L chondrite asteroid at Earth (radius = 6,371,000 m; avg density = 5513 kg m -3 ) can be made by calculating the solid body Roche Limit using the density of L chondrites (3350 kg m -3 ), and the liquid body Roche Limit (approximating a cohesionless rubble pile) using the measured density of Itokawa (1900 kg m -3 ), which is thought to be comprised of low metal ordinary chondrite material (Fujiwara et al., 2006). ...
... The Roche Limit for a solid L chondrite body (bulk density 3350 kg m -3 (Britt and Consolmagno, 2003) is 3106 km above the Earth's surface (9477 km from the center), whereas that for a rubble-pile asteroid is far greater. For S-class rubble pile asteroid Itokawa it would be ~15,800 km above the surface (22,171 km from the center; density from (Fujiwara et al., 2006) and assuming cohesionless rubble; a precise value cannot be calculated without knowing the asteroid shape and internal cohesion properties). Within this transition zone between the rubble pile and the solid body Roche Limit, a body consisting of a power law collection of fragments (as expected for a rubble pile (Sánchez and Scheeres, 2014) would break up and disperse, with abundant miniscule fragments forming a ring, and the largest solid fragments forming moonlets (see also Hyodo et al., 2017). ...
... To date, the smallest asteroid that has been observed globally in detail by a spacecraft up close is Itokawa, with an average size of ∼350 m (A. Fujiwara et al. 2006). Following the Double Asteroid Redirection Test (DART), Dimorphos provides another data point for objects in the 150 m diameter range, even though only one side of Dimorphos was seen in detail (R. T. Daly et al. 2023). ...
Asteroid impacts potentially represent a substantial threat to humanity, but one that we can plan for and mitigate. To design an effective asteroid mitigation mission, however, it is important to have as detailed knowledge of the asteroid threat as possible. Our understanding of a newly discovered object will generally derive from our understanding of the near-Earth object population, and in cases where there is no time for a reconnaissance mission prior to deflection or disruption, we may need to lean heavily on any existing data of similar objects. The Tour of Asteroids for Characterization Observations (TACO) mission concept would fill key gaps in the characterization knowledge needed to plan an effective response to an asteroid threat. A tour targeting potentially hazardous asteroids and focused on reconnaissance objectives specifically relevant for planetary defense would also test instruments and technologies (e.g., autonomous navigation, high-rate gimbals) ahead of when they are actually required in response to a threat. Testing these capabilities is identified as a need in the National Near-Earth Object Preparedness Strategy and Action Plan. The TACO tour concept is specifically designed to measure the most important asteroid properties for planetary defense, including mass, size/shape, surface and near-surface structure, presence of satellites, and composition. These measurements can be obtained using a nominal payload, including a narrow-angle camera, a thermal infrared imager, and deployed test masses for gravity science.
... Shortly before the impact, DART acquired and transmitted high-resolution images of both asteroids. The data revealed complex surfaces with several types of terrains and morphological features like craters and boulders (O. S. Barnouin et al. 2023; R. T. , similar to those previously observed on other asteroids (e.g., Itokawa, A. Fujiwara et al. 2006; Bennu, O. Barnouin et al. 2019;Ryugu, S. Watanabe et al. 2019). ...
... J. Varnes 1976). While this approach has been successful for previous asteroids (e.g., 25143 Itokawa, A. Fujiwara et al. 2006;21 Lutetia, N. Thomas et al. 2012;162173 Ryugu, S. Sugita et al. 2019;101955 Bennu, O. Barnouin et al. 2019), it is very time-consuming and may suffer from human biases that are not easy to quantify. To alleviate this issue, automated methods can be considered to serve as initial guidance and obtain the first assessment of the surface morphology. ...
... It is well-known from previous missions that the surface of a single small body can present a large variability in roughness, typically seen as varying surface texture. Prominent examples are the localized fine-grained deposits on 433 Eros (P. C. Thomas et al. 2002) or the Muses Sea smooth terrain on 25143 Itokawa (A. Fujiwara et al. 2006); both areas contrast with their rougher surroundings. More recent studies, using high-resolution laser altimetry, are available for asteroids Eros (H. C. Susorney & O. S. Barnouin 2018) and Bennu (M. ...
Morphological mapping is a fundamental step in studying the processes that shaped an asteroid surface. However, it is challenging and often requires multiple independent assessments by trained experts. Here we present fast methods to detect and characterize meaningful terrains from the topographic roughness: entropy of information, and local mean surface orientation. We apply our techniques to Didymos and Dimorphos, the target asteroids of NASA's Double Asteroid Redirection Test mission—the first attempt to deflect an asteroid. Our methods reliably identify morphological units at multiple scales. The comparative study reveals various terrain types, signatures of processes that transformed Didymos and Dimorphos. Didymos shows the most heterogeneity and morphology that indicate recent resurfacing events. Dimorphos is comparatively rougher than Didymos, which may result from the formation process of the binary pair and past interaction between the two bodies. Our methods can be readily applied to other bodies and data sets.
